DocID025983 Rev 1

9/14

UM1737

Theoretical and practical measurements

14

Figure 8 and Figure 9 show the error contribution of each parameter to overall error for case

1 and case 2.

For a low Isense/Isense_max the error is mainly due to the saturation. When

Isense/Isense_max increases, the error is mainly caused by the Vio. After this, the most

significant error contribution is caused by the inaccuracy of the shunt resistor. Finally, when

Isense/Isense_max is high, close to or above the upper rail of the amplifier, the maximum

error contribution is the saturation.

The error due to the AVD parameter has not been taken into consideration in this document,

because it is negligible. If the schematic gain equals 470 (gain used for the measurements)

and the AVD equals 120 dB, there is an inaccuracy of 0.047%.

Equation 7 demonstrates this.

Figure 6. Output voltage vs. Isense/Imax using

an alternative op amp

Figure 7. Absolute error on the output voltage

vs. Isense/Imax using an alternative op amp

100m

1

10

100

1E-3

0.01

0.1

1

10

Isense/Isense_max (%)

Vout_max

Vout_min

Vout_opamps

100m

1

10

100

0.01

0.1

1

10

100

1000

10000

Error on opamps output

Theoretical maximum error

Isense/Isense_max (%)

Figure 8. Contribution of each parameter to

overall error for the TSZ121

Figure 9. Contribution of each parameter to

overall error for a 1 mv Vio op amp

0.1

1

10

100

0

20

40

60

80

100

TSZ121

Isense/Isense_max (%)

Saturation

Rs accuracy

Rf and Rg accuracy

Iio

Vio

0.1

1

10

100

0

20

40

60

80

100

1mV Vio op-amp

Isense/Isense_max (%)

Saturation

Rs accuracy

Rf and Rg accuracy

Iio

Vio